갈고닦다 — literally 'grind and polish' — is a set compound for honing a skill through long practice, and five of these eight lines use it: 갈고 닦은 기타 실력으로 'with his hard-honed guitar skills', 자신의 무기를 갈고닦아 'sharpening your own weapon'. The literal sense is here too: 걸레 적셔서 꽉 짜고 닦아요 'wet the cloth, wring it out well, then wipe'.